While it currently sports the highest stats, its "Heal on Spark" is often unneeded (and tricky with only 5 units), and "boosts BB gauge when x damage is taken" requires you to take a heavy beating every turn in order to keep the sustain going.
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Since both gold ubb weapons add critical hit rate, I believe sticking to dual autowarriors is the way to go for this map. (for damage and BB sustain purposes)

Though, if you're willing to farm a bunch, I'd recommend crafting a Holy Beacon LS sphere and upgrading it-- Once map five hits its final upgrade pretty much makes it the definitive mitigation LS sphere for SArc and is often used for some of map 5's ex dungeons.